This invention relates to the field of liquid filters, of the type commonly known as paper towel or toilet paper filters.
It has long been known that very fine filtration can be obtained, removing particulate contaminants from liquids, by flowing the liquids along an extended filter path across the surface formed between two adjoining sheets of filtration material. This filter action is in distinction to the more common filter action in which a liquid is forced through a membrane or porous material; in the latter case, proper filtration requires very careful design of the membrane, and the size of the particles successfully filtered is a function of membrane porosity and the uniformity of the membrane.
The usual form of the first above described filters is the axial flow, wound fibrous tissue filters, popularly known as paper towel filters. These filters use the filtration capability inherent in passing a fluid axially along the surface between two tightly adjoining sheets of fibrous tissue. The fluid does not pass through any given sheet and thus the normal manufacturing tolerances inherent in membrane or porous filters are not required. Significant work has been done on the design of such filters, because of the low cost and widespread availability of filter media in the form of commercially available paper towels, or toilet paper rolls. The disadvantage of all these filters is that such filter media are not designed or manufactured to be used in a filter and thus are neither dimensioned nor structured for this purpose.
As a result, significant effort has been expended in sealing elements of such filter media against bypass flow and in supporting such elements to provide the appropriate filtering action.
Such filters are shown in, for instance, S. K. Yee, et al, U.S. Pat. No. 3,308,957, the Frantz filter, which is considered prototypical of the paper towel or toilet paper filter, and U.S. Pat. No. 3,504,803 to Brayman and U.S. Pat. No. 4,017,400 to Schade.
Each such patent discloses an axially wound roll of filter material described generally as being a paper towel or toilet paper roll, the rolls subsisting upon a supporting cardboard tube (for instance, the Yee patent, Item 35). This tube is supported contactingly by an inner cylinder or rod pipe axially extending within the filter canister, which forms one of the flow paths for the oil to be filtered. Various forms of plates, gaskets or knife edge seals are then depressed into the end of the roll to restrict the flow of fluid to an axial path through the papers of the towel, avoiding bypass conditions.